Skip to content Skip to navigation

Connexions

You are here: Home » Content » Plotting MOS I-V

Navigation

Content Actions
  • Download module PDF
  • Add to ...
    Add the module to:
    • My Favorites
    • A lens
    • An external social bookmarking service
    • My Favorites (What is 'My Favorites'?)
      'My Favorites' is a special kind of lens which you can use to bookmark modules and collections directly in Connexions. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need a Connexions account to use 'My Favorites'.
    • A lens (What is a lens?)

      Definition of a lens

      Lenses

      A lens is a custom view of Connexions content. You can think of it as a fancy kind of list that will let you see Connexions through the eyes of organizations and people you trust.

      What is in a lens?

      Lens makers point to Connexions materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

      Who can create a lens?

      Any individual Connexions member, a community, or a respected organization.

    • External bookmarks
  • E-mail the author

Lenses

What is a lens?

Definition of a lens

Lenses

A lens is a custom view of Connexions content. You can think of it as a fancy kind of list that will let you see Connexions through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to Connexions materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual Connexions member, a community, or a respected organization.

This content is ...

In these lenses

  • Printable Books

    This module is included inLens: Connexions Books Available for Print on Demand
    By: ConnexionsAs a part of collection:"Introduction to Physical Electronics"

    Comments:

    "This book is available print on demand by going to the course page and selecting "Order a printed copy"."

    Click the "Printable Books" link to see all content selected in this lens.

Recently Viewed

Tags

(What is a tag?)

These tags come from the endorsement, affiliation, and other lenses that include this content.

Plotting MOS I-V

Module by: Bill Wilson

Summary: Plotting MOS I-V, and sketching the I-V behavior.

Now we use two of the equations ((Reference) and (Reference)) that we found in the discussion about MOS Regimes to calculate a set of Vdsat Vdsat and Idsat Idsat values for various value of Vgs Vgs . (Note that Vgs Vgs must be greater than VT VT for the two equations to be valid.) When we get the numbers, we build a little table.

Once we have the numbers, then we sketch a piece of graph paper with the proper scale, and plot the points on it. Once the Idsat Idsat , Vdsat Vdsat points have been determined, it is easy to sketch in the I-V behavior. You just draw a curve from the origin up to any given point, having it "peak out" just at the dot, and then draw a straight line at Idsat Idsat to finish things off. One such curve is shown in Figure 3. And then finally in Figure 4 they are all sketched in. Your curves probably wont be exactly right but they will be good enough for a lot of applications.

Figure 1: Results of calculating Vdsat Vdsat and Idsat Idsat .
V gs V gs V dsatV V dsat V V dsatmAV dsat mA
3 1 0.44
4 2 1.76
5 3 3.96
6 4 7.04
7 5 11
Figure 2: Plotting Idsat Idsat and Vdsat Vdsat .
Figure 2 (4.25.png)
Figure 3: Sketching in one of the I-V curves.
Figure 3 (4.26.png)
Figure 4: The complete set of curves.
Figure 4 (4.27.png)

There is a particularly easy way to measure by kk and VT VT for a MOSFET. Let's first introduce the schematic symbol for the MOSFET, it looks like Figure 5. Let's take a MOSFET and hook it up as shown in Figure 6.

Figure 5: Schematic symbol for a MOSFET
Figure 5 (4.28.png)
Figure 6: Circuit for finding VT VT and kk
Figure 6 (4.29.png)

Since the gate of this transistor is connected to the drain, there is no doubt that V gs - V ds V gs V ds is less than VT VT . In fact, since V gs = V ds V gs V ds , their difference, is zero. Thus, for any value of Vds Vds , this transistor is operating in its saturated condition. Since V gs = V ds V gs V ds , we can rewrite a previous equation derived equation from the section on MOS transistor as

I d =k2 V ds - V T 2 I d k 2 V ds V T 2 (1)

Now let's take the square root of both sides:

I d =k2 V ds - V T I d k 2 V ds V T (2)

So if we make a plot of I d I d as a function of Vds Vds , we should get a straight line, with a slope of k2 k 2 and an x-intercept of VT VT .

Figure 7: Obtaining VT VT and kk
Figure 7 (4.30.png)

Because of the expected non-ideality, the curve does not go all the way to VT VT , but deviates a bit near the bottom. A simple linear extrapolation of the straight part of the plot however, yields an unambiguous value for the threshold voltage VT VT .

Comments, questions, feedback, criticisms?

Send feedback